Effect of bowel preparation completion time on bowel cleansing efficacy: Prospective randomized controlled trial of different bowel preparation completion times precolonoscopy

Objectives: The elapse time between the completion of bowel cleansing and colonoscopy is one of the important factors for proper bowel cleansing. Although several studies have reported that a short time interval resulted in a favorable bowel cleansing, no randomized controlled trial (RCT) has been conducted to determine the effect of the elapse time. Consequently, we performed an RCT to investigate the efficacy of bowel preparation of participants who underwent colonoscopy according to the different time intervals between the completion of bowel preparation and colonoscopy. Methods: In this single-center RCT, study participants were randomized to complete bowel preparation either 2–4 h or 4–8 h before colonoscopy. The primary end-point was successful bowel preparation, rated using the Boston Bowel Preparation Scale (BBPS). Results: A total of 504 individuals were included (2–4 h, 255; 4–8 h, 249). The rate of successful bowel preparation in the 2–4 h group showed noninferiority compared with that of the 4–8 h group (97.6% vs. 95.2%; rate difference, 2.5% [−0.8% to 5.7%]; P_{for noninferiority} < 0.001, P_{for superiority} = 0.136). The rate for perfect cleansing (a BBPS score of 9) was higher in the 2–4 h group (56.5% vs. 39.8%, P < 0.001). Conclusion: When bowel cleansing was finished 2–4 h before the start of colonoscopy, the overall bowel cleansing was noninferior, and perfect cleansing was superior, compared to that when cleansing was finished 4–8 h before colonoscopy.